Axonal transport of NADPH-diaphorase and [H-3]nitro-L-arginine binding, but not [H-3]cGMP binding, by the rat vagus nerve

Previous studies have shown that the NO.-cGMP pathway may be functionally r elevant in the nodose ganglion and at afferent terminations of the vagus ne rve. The technique of unilateral vagal ligations, using double ligatures, w as combined with the techniques of NADPH-diaphorase histochemistry, as an i ndex of nitric oxide synthase (NOS) activity, and autoradiography using the radioligands [H-3]nitro-L-arginine and [H-3]cGMP, to examine axonal transp ort of NOS and cGMP-dependent effectors by the rat vagus nerve. A populatio n of perikarya in the nodose ganglia was NADPH-diaphorase positive, and bin ding of both [H-3]nitro-L-arginine and [H-3]cGMP was found on the nodose ga nglia. Following vagal ligation, NADPH-diaphorase reactivity accumulated pr oximal to the proximal ligature and distal to the distal ligature. Vagus ne rve transection beyond the distal ligature eliminated NADPH-diaphorase reac tivity at the distal ligature. Similarly, [H-3]nitro-L-arginine binding was found over the nodose ganglion; and after vagal ligation, an accumulation of [H-3]nitro-L-arginine binding was seen adjacent to the proximal ligature , though little binding was found adjacent to the distal ligature. No accum ulation of [H-3]cGMP binding was found adjacent to either the proximal or t he distal ligatures. These findings suggest that the rat vagus nerve bidire ctionally transports NOS, the enzyme involved in biosynthesis of NO. by nit roxidergic nerves. As anticipated, [H-3]nitro-L-arginine, a competitive inh ibitor of the amino acid precursor for NO.- binds only to a centrifugally t ransported moiety that we conjecture is NOS, while cGMP apparently is not s ubject to transport. These data further support the use of NO. in transmiss ion at vagal afferent terminals. (C) 2000 Elsevier Science B.V. All rights reserved.